Color cathode ray tube with temperature-responsive color purity magnets

ABSTRACT

A color cathode ray tube arrangement wherein a temperature responsive magnetic device which comprises a permanent magnet element and a magnetic element having temperature responsive variable permeability is provided on a color cathode ray tube to compensate for beam mislanding on the color phosphor screen of the color cathode ray tube caused by thermal expansion of a beam selecting mask in the tube thereby to maintain fine color purity.

United States Patent Machida et al.

COLOR CATHODE RAY TUBE WITH TENIPERATURE-RESPONSIVE COLOR PURITY MAGNETSInventors: Hiromasa Machida, Tokyo; Noboru Yamaguchi, Yokohama, both ofJapan Assignee: Sony Corporation, Tokyo, Japan Filed: Feb. 2, 1973 Appl.No.: 329,049

Foreign Application Priority Data Feb. 3, 1972 Japan 47-14377 US. Cl.313/412; 313/437; 335/212 Int. Cl. H01J 29/07; H01] 29/51 Field ofSearch... 313/75; 313/79; 313/70C; 313/84[USOnly1 313/84; 335/217References Cited UNITED STATES PATENTS 2/1961 Clay 313/84 X 1 1 Aug. 12,1975 3,296,570 1/1967 Uetake et a1. 313/84 x 3,512,035 5/1970 Egawa Cl21]. 313/75 x 3,573,525 4/1971 Fuse 335/217 3,623,151 11/1971 [keuchi335 217 FOREIGN PATENTS OR APPLICATIONS 1,199,891 9/1965 Germany 313/75Primary Examiner-Robert Segal Attorney, Agent, or Firm-Lewis H.Eslinger; Alvin Sinderbrand l 5 7 ABSTRACT A color cathode ray tubearrangement wherein a temperature responsive magnetic device whichcomprises a permanent magnet element and a magnetic element havingtemperature responsive variable permeability is provided on a colorcathode ray tube to compensate for beam mislanding on the color phosphorscreen of the color cathode ray tube caused by thermal expansion of abeam selecting mask in the tube thereby to maintain fine color purity.

4 Claims, 11 Drawing Figures PATENTED AUG 7 2 I975 SHEET COLOR CATHODERAY TUBE WITH TEMPERATURE-RESPONSIVE COLOR PURITY MAGNETS BACKGROUND OFTHE INVENTION l. Field of the Invention This invention relates generallyto means for avoiding beam mislanding in a color cathode ray tube havinga color phosphor screen, and more particularly to means of compensatingfor such mislanding caused by temperature variations in the colorcathode ray tube.

2. Description of the Prior Art In a conventional color cathode ray tubethere is a mask which has a number of slits or small aperturestherethrough to allow the electron beams to reach, or land on, only thephosphor elements that emit light of selected colors. In such tubes,heat is generated by the impingement of the electron beams on the mask.This heat causes thermal expansion or distortion of the mask with theresult that the positions of the slits or apertures are shifted relativeto the phosphor elements of the screen. This causes the landingpositions of the electron beam on the color phosphor screen to shift,and the mislanding of the electron beams, in turn. causes deteriorationsin color purity. The mislanding of the electron beam is worse near theperiphery of the screen than at the center and is particularlyobjectionable in the case of wide angle beam scanning tubes.

Several ways have been proposed to compensate for thermally-inducedelectron beam mislanding. One conventional system is to hold the mask bya bimetallic support to change the position of the mask in the tuberelative to the screen in response to temperature change. Anothercompensating system uses an auxiliary beam deflection coil in additionto the main deflection coil. The current in the auxiliary beamdeflection coil is changed in response to the mask temperature to changethe electron beam path in order to avoid the mislanding of the electronbeams.

However. the conventional systems mentioned above have severaldrawbacks. They are complicated in con struction, they require a numberof parts, and they are expensive.

Accordingly, an object of this invention is to provide a color cathoderay tube arrangement which maintains excellent color purity with simplecorrecting means for compensating for temperature-caused deterioration'sin color purity.

Another object of this invention is to provide a color cathode ray tubearrangement wherein mislanding of electron beams on the screen of thecolor cathode ray tube caused by temperature variations in the mask andscreen is compensated for by simple correcting means that may be locatedon the funnel portion of the tubev Still another object of thisinvention is to provide a color cathode ray tube arrangement in whichtemperature-induced mislanding of the electron beams is prevented by atemperature-responsive permanent magnetic device of simple construction.

A further object of this invention is to provide a simple color-puritycorrecting means comprising a temperature-responsive permanent magneticdevice.

SUMMARY OF THE INVENTION According to this invention, a color cathoderay tube arrangement for compensating for electron beam mislandingcomprises a temperature-responsive magnetic device. the magnetic fluxdensity of which changes in response to temperature variation. Themagnetic compensating means is located at a predetermined positionbetween the beam deflection center of the tube and the screen in orderto modify by the magnetic flux originated from the magnetic device thepaths of the beams.

Various devices may be used as the temperatureresponsive magneticdevice. An example of such a temperature-responsive magnetic device is apermanent magnet which will change magnetic flux originated therefrom inresponse to temperature changes. A preferable example is a combinationof a normal permanent magnet and a temperature-responsive magneticmaterial whose permeability changes in response to temperature changes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of one exampleof a temperature-responsive magnetic device employed in a color cathoderay tube temperature compensating arrangement according to theinvention.

FIG. 2 is a cross-sectional view of the device shown in FIG. 1.

FIG. 3 is a graph that shows the temperatureresponsive characteristic ofthe device shown in FIGS. 1 and 2.

FIGS. 4 and 5 are perspective views illustrating the color cathode raytube temperature compensating arrangements according to the invention.

FIG. 6 is a cross'sectional view of a fragment of the color cathode raytube arrangements depicted in FIGS. 4 and 5.

FIGS. 7 to 10, inclusive, are diagrams for explaining compensation formislanding of electron beams by means of the invention.

FIG. 11 is a perspective view of another example of the color cathoderay tube arrangement according to the invention with a section of thetube broken away to show the interior construction thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show anembodiment of a temperature-responsive magnetic device 1 used inaccordance with this invention. The device I designates generally atemperature-responsive magnetic device which consists of a permanentmagnet 2 and a temperatureresponsive magnetic material 3. The permanentmagnet 2 is made of, for example, Ba-ferrite containing BaCO and Fe O inthe ratio of 15:85 by mol.% and may be formed as a disc magnetized alongits diameter. The temperature-responsive magnetic material 3 may be madeof Mn Zn-ferrite and formed as a disc having a recess bounded by anannular projection at the periphery of one surface. The disc 3 has amagnetic permeability that decreases as the temperature increases. Anexample of a suitable material for the disc 3 is a MnZn-ferrite composedof Fe O MnCO and ZnO combined in the ratio of 50:27:23 by mol.%. In thiscase, when the permanent magnet 2 is fitted to the recess in thetemperature-responsive magnetic material 3, one side of the permanentmagnet 2 and its periphery are covered with the magnetic material 3.

With such an arrangement, since the permeability of the magneticmaterial 3 is high when temperature is low, the magnetic flux thatoriginates in the permanent magnet 2 is almost completely shunted by themagnetic material 3 with the result that the magnetic flux density ofthe external magnetic field produced by the magnetic device I is low. Onthe other hand, when the temperature becomes high, the permeability ofthe magnetic material 3 is reduced, with the result that the magneticflux density of the external magnetic field of the magnetic device 1becomes high due to the fact that the magnetic flux from the magnet 2 isless shunted by the magnetic material 3. Accordingly, it will beunderstood that the relationship between the temperature and the fluxdensity of the external magnetic field from the magnetic device 1 can bemade such as shown in the graph of FIG. 3 in which the ordinaterepresents the magnetic flux density in Gauss and the abscissatemperature in C.

It is not necessary that the permanent magnet 2 and thetemperature-responsive magnetic material 3 used in the device 1 belimited to the configurations mentioned above. They can be formed, forexample, with rectangular perimeters with one side of the permanentmagnet and its rectangular perimeter covered by the magnetic material.Other polygonal forms may also be used.

Four temperature-responsive magnetic devices 1, each of which isconstructed as mentioned above, are mounted on a color cathode ray tube4 at the corners of its funnel portion 4F, as shown in FIG. 4. In thecase of a color cathode ray tube provided with a beam selecting maskhaving a number of vertical slits and a phosphor screen in whichrespective sets of color phosphor strips extended in the verticaldirection are arranged successively along the horizontal beam scanningdirection, a shift of the landing position of the electron beams in thehorizontal scanning direction, namely in the left and right direction,becomes a problem that must be corrected. Accordingly, it may bepossible in such a case that further temperature-responsive magneticdevices similar to the device 1 in FIG. 1 be mounted on the tube at themid-portion of the right and left peripheral sides of the funnel portion4F, respectively, in addition to those mounted at the corners thereof,as shown in FIG. 5. Further, it may be possible in a color cathode raytube with a shadow mask that additional temperature-responsive magneticdevices similar to the devices I be mounted on the tube at themidportion of the upper and lower peripheral portions of the funnelportion 4F thereof at the positions 1 as indicated in FIG. 5 in brokenlines.

It is preferred that the respective temperatureresponsive magneticdevices 1 be mounted on the tube 4 in such a manner that the sidesurface of each permanent magnet 2 which is not covered with thetemperature-responsive magnetic material 3 faces away from the tube, asshown in FIG. 6.

FIGS. 7 and 8 illustrate how mislanding of electron beams may beprevented by mounting the temperature responsive magnetic device I inthe manner described above. In the case where the magnetic device 1 hasthe characteristic such as is shown in FIG. 3 and is mounted on thefunnel portion 4F of the tube 4 in a manner to make the magnetizeddirection of the permanent magnet 2 perpendicular to the plane of thesheet of FIG. 7, the magnetic field H+ produced by the permanent magnet2 will be directed into the plane of the drawing in the tube 4, asindicated by the X within the circle. With such an arrangement, if thereis no magnetic flux, an electron beam 5 deflected by a deflection coil(not shown) follows the path shown by the solid line in FIG. 7, while ifthere is a magnetic field H+ produced by the device I, the electron beam5 is subjected to a force designated by an arrow F+ and is deflected tothe path shown by the broken line.

It is assumed that a typical vertical slit or aperture 6a of the beamselecting mask is positioned as shown in FIG. 8 at room temperature. Anelectron beam having passed through a virtual deflection center 7 on thetube axis 8 follows along a path shown by the solid line 50 through theaperture 6a. When the temperature increases, the position of theaperture is shifted to the position 6b. In order to pass through theaperture in this new location, the electron beam follows a path shown bythe solid line 5b in FIG. 8. When the magnetic device is mounted on thetube 4, the electron beam is deflected a little as shown by the brokenline 5A at room temperature because the magnetic field I-I+ produced bythe magnetic device 1 is weak at room temperature as described above. Onthe other hand, the magnetic field I-I-lincreases as the temperatureincreases, so that the electron beam is deflected more, as shown by thebroken line 58. As a result, the electron beam lands at substantiallythe same position on the phosphor screen 9 irrespective of temperaturechanges that cause thermal expansion or distortion of the beam selectingmask. It will be easily realized that the electron beams directed alongother paths will also land on respective constant positions on thescreen.

It is also possible to use a temperature-responsive magnetic materialhaving a different characteristic such that, as the temperatureincreases, the permeability also increases. If the material having sucha characteristic is employed as the magnetic material 3, thetemperature-responsive magnetic device 1 has a relationship between themagnetic flux density and temperature that is the reverse of that shownin FIG. 3. That is to say, as the temperature goes down, the magneticflux density of the external magnetic field from the magnetic device 1increases, while as the temperature rises, the magnetic flux densitydecreases. Mislanding of electron beams can also be prevented by the useof such a temperature-responsive magnetic device I. With reference toFIGS. 9 and 10, such a case will now be described.

In FIG. 9 the temperature-responsive magnetic device 1 is mounted on thetube 4 in such a manner that the magnetic field I-I- from the magneticdevice I passes through the tube 4 in the direction into the plane ofthe drawing. This is opposite to the direction of the flux H+ in FIG. 7.With such an arrangement the electron beam 5 is subjected to the forceshown by an arrow F- by the magnetic field H- and hence is deflected asshown by the broken line in FIG. 9. Accordingly, as shown in FIG. 10,the electron beam having passed through the virtual deflection center 7on the tube axis 8, is deflected more at room temperature, as shown bythe broken line 5A, since the magnetic field H- is greatest when thetube structure is at room temperature. On the other hand, since themagnetic field H- decreases as the temperature increases, the electronbeam is deflected less as shown by the broken line 5B in FIG. 10.Accordingly, it will be understood that in this case the landingposition of the electron beam 5 on the phosphor screen 9 of the tube 4is kept constant irrespective of thermal expansion or distortion of thebeam selecting mask due to temperature variations.

It will be also realized that the electron beams travelling along theother paths land on the phosphor screen at respective constant positionsas in the above case without illustrating them.

The temperature responsive magnetic device 1 is not restricted to beingmounted on the funnel portion 4F of the tube 4, but it may be mounted ona holder of the deflection coil or a frame for the beam selecting mask 6inside the tube 4 with the same effect mentioned above. In the case ofmounting the device 1 on the frame 10, variation in temperature of thebeam selecting mask 6 can be directly detected by the magnetic device I.

With the color cathode ray tube arrangement of this invention describedas above, mislanding of electron beams caused by thermal expansion ofdistortion of the beam selecting mask can be avoided to maintainexcellent color purity.

We claim as our invention:

1. A color cathode ray tube arrangement comprising:

A. a color cathode ray tube comprising:

l. a color phosphor screen comprising areas arranged in a predeterminedpattern to emit light of different colors when struck by electrons,

2. electron beam generating means to direct electron beams at saidscreen, and

3. a beam selecting element disposed near said screen comprisingelectron passages positioned relative to said areas to allow saidelectron beams to land on predetermined areas of said screen accordingto the directions along which said beams pass through said passages; and

B. temperature responsive magnetic means provided on said tube forcompensating for mislanding of said electron beams on incorrect ones ofsaid areas of said screen due to thermal expansion of said beamselecting element resulting in displacement of at least some of saidpassages relative to their respective areas of said screen, saidtemperature responsive magnetic means comprising:

1. a permanent magnet, and

2. a magnetic shunt element having temperature responsive variablepermeability, said magnetic shunt element forming a path for at least apart of the magnetic flux originating in said permanent magnet and beinglocated on said tube to be heated by heat from said beam selectingelement to change the intensity of magnetic flux from said magneticmeans with temperature variations in said tube to cause the path of saidelectron beams landing on the screen to change in response to saidthermal expansion of the beam selecting element thereby to maintainexcellent color purity of light emitted by said screen, said magneticelement being formed into a block-like shape having a recess on onesurface, and said permanent magnet being placed in said recess.

2. A color cathode ray tube arrangement according to claim 1, whereinsaid magnetic element is formed into a disc shape having a pair ofopposite flat surfaces one of which is provided with said recess thereinand said permanent magnet is also formed into a disc shape having a pairof opposite flat surfaces and placed in said recess with one of saidflat surfaces of said magnet exposed to the outside.

3. A color cathode ray tube arrangement according to claim 1, whereinsaid tube comprises a funnel portion and said temperature responsivemagnetic means is attached to the outer surface of said funnel portion.

4. A color cathode ray tube arrangement according to claim 1, whereinsaid temperature responsive magnetic means is attached to said beamselecting element in said tube.

1. A color cathode ray tube arrangement comprising: A. a color cathoderay tube comprising:
 1. a color phosphor screen comprising areasarranged in a predetermined pattern to emit light of different colorswhen struck by electrons,
 2. electron beam generating means to directelectron beams at said screen, and
 3. a beam selecting element disposednear said screen comprising electron passages positioned relative tosaid areas to allow said eLectron beams to land on predetermined areasof said screen according to the directions along which said beams passthrough said passages; and B. temperature responsive magnetic meansprovided on said tube for compensating for mislanding of said electronbeams on incorrect ones of said areas of said screen due to thermalexpansion of said beam selecting element resulting in displacement of atleast some of said passages relative to their respective areas of saidscreen, said temperature responsive magnetic means comprising:
 1. apermanent magnet, and
 2. a magnetic shunt element having temperatureresponsive variable permeability, said magnetic shunt element forming apath for at least a part of the magnetic flux originating in saidpermanent magnet and being located on said tube to be heated by heatfrom said beam selecting element to change the intensity of magneticflux from said magnetic means with temperature variations in said tubeto cause the path of said electron beams landing on the screen to changein response to said thermal expansion of the beam selecting elementthereby to maintain excellent color purity of light emitted by saidscreen, said magnetic element being formed into a block-like shapehaving a recess on one surface, and said permanent magnet being placedin said recess.
 2. electron beam generating means to direct electronbeams at said screen, and
 2. a magnetic shunt element having temperatureresponsive variable permeability, said magnetic shunt element forming apath for at least a part of the magnetic flux originating in saidpermanent magnet and being located on said tube to be heated by heatfrom said beam selecting element to change the intensity of magneticflux from said magnetic means with temperature variations in said tubeto cause the path of said electron beams landing on the screen to changein response to said thermal expansion of the beam selecting elementthereby to maintain excellent color purity of light emitted by saidscreen, said magnetic element being formed into a block-like shapehaving a recess on one surface, and said permanent magnet being placedin said recess.
 2. A color cathode ray tube arrangement according toclaim 1, wherein said magnetic element is formed into a disc shapehaving a pair of opposite flat surfaces one of which is provided withsaid recess therein and said permanent magnet is also formed into a discshape having a pair of opposite flat surfaces and placed in said recesswith one of said flat surfaces of said magnet exposed to the outside. 3.A color cathode ray tube arrangement according to claim 1, wherein saidtube comprises a funnel portion and said temperature responsive magneticmeans is attached to the outer surface of said funnel portion.
 3. a beamselecting element disposed near said screen comprising electron passagespositioned relative to said areas to allow said eLectron beams to landon predetermined areas of said screen according to the directions alongwhich said beams pass through said passages; and B. temperatureresponsive magnetic means provided on said tube for compensating formislanding of said electron beams on incorrect ones of said areas ofsaid screen due to thermal expansion of said beam selecting elementresulting in displacement of at least some of said passages relative totheir respective areas of said screen, said temperature responsivemagnetic means comprising:
 4. A color cathode ray tube arrangementaccording to claim 1, wherein said temperature responsive magnetic meansis attached to said beam selecting element in said tube.